This invention relates to antenna elements and particularly to such elements which are formed by means of a dipole reactively coupled to a microstrip line; and to arrays of such elements.
It is generally accepted by antenna designers that a radiating dipole antenna element disposed close to a ground plane and driven by a conventional transmission line will have poor radiation efficiency, and a narrow bandwidth. One reason it has been assumed that the efficiency of such antenna configurations would be low is the general belief that large dipole currents and hence high resistive losses would result from interaction with the radiation reflected from the ground plane. Also, since the fields of the currents which do not radiate are trapped as stored energy it has been assumed that a narrowing of the operational bandwidth of the antenna would result. For example, such a narrowing of the bandwidth would seem to follow from the accepted design equation: .omega.U/P = f/2.alpha.f; where 2.alpha.f is the bandwidth; .omega. is 2.pi.f; U is the stored energy and P is the radiated power. Hence, one would conclude that the bandwidth decreases as the stored power increases, i.e. 2.alpha.f .DELTA. 1/U.